Effect of tuberculin skin test on ex-vivo interferon-gamma assay for latent tuberculosis infection

Jung Yeon Lee, Hee Jin Choi, Sang Nae Cho, I. Nae Park, Yeon Mok Oh, Sang Do Lee, Woo Sung Kim, Dong Soon Kim, Won Dong Kim, Tae Sun Shim

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1 Citation (Scopus)


Background: Recently, two commercialized whole-blood assays, QuantiFERON®-TB Gold (QFT) and T SPOT-TB® (SPOT), which measure the IFN-γ released in the whole blood after being incubation with mycobacterial antigens, were approved for the diagnosis of a latent tuberculosis infection (LTBI). However, there is data on whether or not the previously used PPD skin tests (TST) have any influence on the diagnostic ability of these ex-vivo IFN-γ assays. Methods: Forty-six 15 year-old students who did not appear to be infected with Mycobacterium tuberculosis were enrolled in this study. The peripheral blood was collected and used for two IFN-γ assays. The IFN-γ assays and TST were performed at the baseline (1st). The TST was repeated two months later (2nd), and the IFN-γ assays were repeated two (2nd) and four months (3rd) later only in those subjects who had negative results at the baseline in both the IFN-γ assays and TST. An induration size > 10 mm was considered to be positive in the TST. Results: The mean TST value was 3.1 ± 5.4 mm (range: 0-20). Of the 46 subjects examined, 13 subjects (28.3%) showed positive results in the two-step TST. Nine (19.6%) were SPOT-positive and only one (2.2%) was QFT-positive. The 2nd and 3rd QFT were carried out in 23 and 25 all-negative subjects, respectively, and all showed negative results. The 2nd SPOT was performed in 23 subjects and only one (4.3%) showed a weak-positive result. Conclusion: Even though there were some discrepancies in the results of the two ex-vivo IFN-γ assays, it appears that their results were not influenced by a previous TST carried out in two or four months earlier.

Original languageEnglish
Pages (from-to)406-412
Number of pages7
JournalTuberculosis and Respiratory Diseases
Issue number4
Publication statusPublished - 2005 Oct

All Science Journal Classification (ASJC) codes

  • Pulmonary and Respiratory Medicine
  • Infectious Diseases


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